Caracterização geológica das rochas metamáficas metaultramáficas entre os distritos Corrégo do brejão e Altinho – Coromandel (MG)

Abstract

Mafic-ultramafic rock associations are rare in the Earth's crust, however they are of great importance due to their economic potential and geotectonic significance. In the region of the municipality of Monte Carmelo-MG, metamafic and metaultramafic rocks appear near the limits of the Granitic Complex Monte Carmelo, which according to the works carried out in this area are attributed to the Complexo Abadia dos Dourados, of Brazilian age, and the ultramafic rocks being derived from an alkaline magmatism of the Mata da Corda Group, of Cretaceous age. However, no specific studies have been developed on these rocks, discussing whether metamafic and metaultramafic orthoderived rocks associated with the Araxá Group could occur, or whether these rocks could constitute metamafic-metaultramafic associations. Thus, the work aimed to develop a study on metamafic and metaultramafic rocks that outcrop to the east of the Monte Carmelo Granitic Complex, between the districts of Brejão and Altinho de Coromandel (MG). With the mapping, the occurrence of metamafic, metaultramafic or associated bodies was identified, being formed by metadiabases, amphibolites, metaperidotites and chlorite-tremolite galls. The petrography indicated the mineral assemblages formed by: actinolite, biotite chlorite, epidote, hornblende, plagioclase, quartz and tremolite in metamafics and actinolite, olivine, pyroxene, quartz, tremolite and serpentine in metaultramafics. The presence of metamorphic textures helped to identify the rocks, with blastosubophytic texture present in the metadiabase; in the amphibolites, pseudomorphs of plagioclase and textures of consumption of biotite by chlorite are present; the metaperidotite presents relic minerals, being preserved olivines and pyroxene, besides presenting alteration corona texture and mesh textures; in galls chlorite-tremolite porphyroblasts are present. The metamafic and metaultramafic rocks in the study show evidence of metamorphism in the greenschist facies, with a metamorphic peak in the amphibolite facies. The protoliths were identified as orthoderived in metaultramafics and metamafics, and there may be the possibility that part of the amphibolites comes from paraderived rocks, although further studies are necessary for identification.